Feature: Combine model switch + prompt in single command during interactive session

Problem

When switching models mid-conversation for a second opinion (e.g., asking Opus after working in Sonnet), users must:

1. /model opus
2. Type the actual message

This two-step process creates friction, especially when frequently switching models during collaborative work (e.g., brainstorming, reviewing decisions).

Proposed Solution

Allow combining model switch and prompt in a single command. Possible syntaxes:

• @opus What do you think about this?
• /model opus What do you think about this?
• /ask opus What do you think about this?

Use Case

During interactive sessions, users often want a quick second opinion from a different model without permanently switching. A one-shot syntax would make this workflow much smoother.